Injection molding nozzles are widely known in the state of the art. They are used to feed a flowable material such as a plastic melt at a predeterminable temperature and under high pressure to a separable mold insert. In general they comprise a feed pipe fitted with a flow duct terminating in a nozzle orifice. This orifice subtends a discharge aperture issuing through a gate into the mold insert (mold nest). To preclude the flowable material within the feed pipe from cooling prematurely, one or more electric heaters assure(s) a best possible temperature distribution as far as into the nozzle orifice.
The German patent document DE-A-199 41 038 proposes depositing in bonding manner at least one insulating layer and at least one heating stratum by means of direct coating on at least one wall of a feed pipe fitted with a flow duct. Accordingly the heater and the feed pipe are designed integrally, as a result of which the insulating layer of an electrically insulating feed pipe may be eliminated. Illustratively direct coating is carried out using the foil, thick film or screen techniques, such layers being separately or simultaneously baked following their deposition. Depositing the layers in bonding manner accordingly assures a permanent firm affixation to the feed pipe wall and accordingly rigid retention on the hot runner manifold or the hot runner nozzle. Because of the compactness/thinness attained by direct deposition, the heater in turn is very compact, indeed such a design offers extreme compactness. Due to the integral design, the output can be raised considerably because the heating is directly generated and dissipated at the surface of the hot runner element requiring heating. As a result, the heaters, which typically are delicate, are reliably protected against overheating. Again, the nozzle may be heated and cooled rapidly and accurately, this feature being advantageous from the beginning to the end of the production procedure.
An electric junction between the electrical heating tracks and a power source must be created to apply electric power to such a heater. Basically such an electrical junction must meet the following requirements: on one hand it must implement electric contact between the heater and a hookup conductor linked to the electric power source. On the other hand it must be temperature resistant in the light of the high temperatures of injection molding. Also it must withstand mechanical tensile loads and assure inward and outward electrical insulation. Lastly it should be as compact as practical to miniaturize the injection molding nozzle. The last cited requirement is significant indeed for thick film heaters disclosed in the German patent document DE-A-199 41 038.